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#617300 - 29/12/06 12:31 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
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Stolen from another forum:
Quote:
so the conveyor cant stop the plane from moving forward under its own power because it cant move the air that the plane propels itself with. plane will go forward and take off.

True the conveyor will match the speed of the plane but its only pushing against the wheels which do not propel a plane forward or measure speed of the plane.

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#617301 - 29/12/06 12:40 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Since the air is calm, the plane MUST move relative to the ground to get air flowing across it's wings.

The conveyor belt prevents it from moving in relation to the ground.

If the plane is taxiing (sp?), the conveyor belt will STILL keep it from moving.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617302 - 29/12/06 12:42 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
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No, it really won't.

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#617303 - 29/12/06 12:45 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
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Quote:
Originally posted by Mobycat:
The conveyor belt prevents it from moving in relation to the ground.
No, it won't. The tires on the plane spin freely.

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#617304 - 29/12/06 12:45 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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It will.

Again...put a windsock on the wing. It will not flutter.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617305 - 29/12/06 12:52 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
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It is physically not possible for freely rotating wheels to prevent an airplane from moving.

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#617306 - 29/12/06 12:53 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Mobycat:
Since the air is calm, the plane MUST move relative to the ground to get air flowing across it's wings.

The conveyor belt prevents it from moving in relation to the ground.

If the plane is taxiing (sp?), the conveyor belt will STILL keep it from moving.
I swear you're just trolling now. The conveyor can apply a certain amount of friction to the wheels. The prop/turbine can provide much more force (more) directly to the fuselage of the aircraft. The force applied to the bottom of the wheels/tires causes them to spin on their respective axes (axises?) but not hold the fuselage back. Greater thrust than resistance causes the plane to move forward. As the plane moves forward the conveyor speeds up, yet is only causing friction with the bottom of the spinning tires. The prop/turbine is creating greater friction with the air. The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.

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#617307 - 29/12/06 12:54 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
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Quote:
Originally posted by Mobycat:
It will.

Again...put a windsock on the wing. It will not flutter.
Not if the plane isn't moving.

But if the conveyor belt is moving, then the plane is moving. Period. That's in the given problem statement.

And if the plane is moving, then that windsock will be flapping like all hell.

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#617308 - 29/12/06 12:55 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by MattyX:
The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617309 - 29/12/06 12:56 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by porsche996:
Quote:
Originally posted by Mobycat:
[b]It will.

Again...put a windsock on the wing. It will not flutter.
Not if the plane isn't moving.

But if the conveyor belt is moving, then the plane is moving. Period. That's in the given problem statement.

And if the plane is moving, then that windsock will be flapping like all hell.[/b]
OK. Stand next to the plane on the side of the conveyor belt.

In relation to you (which is also in relation to the wind, since it's calm), the plane WILL NOT BUDGE.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617310 - 29/12/06 12:59 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


If the plane moves at all, then it's by the thrust of its engines.

If the plane moves, then the conveyor moves in an opposite direction and speed.

The conveyor only applies rotational force to the wheels of the plane. The rotational force of the wheels is NOT then applied to the thrust of the engines; the two are not linked in any way.

Therefore, the plane moves independent of the wheel rotation, at all times. Hence the reason a plane can fly, yet the wheels are not rotating at all.

Don't make me go Newtonian on your ass...

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#617311 - 29/12/06 01:00 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.[/b]
Just because the conveyor matches the planes speed does not mean that the plane is stationary. I have changed nothing. No matter how fast the conveyor spins, as long as the prop is pushing air it will move forward.

::ETA:: The key is greater friction with the air (caused by the prop/jet turbine pushing air) than friction with the conveyor.

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#617312 - 29/12/06 01:26 PM Re: Know that if you do not post in this thread today the human race may cease to exist
slomatt Offline
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Registered: 10/04/02
Posts: 165
Loc: Bay Area, CA
Quote:
Originally posted by Mobycat:
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.
Mobycat, please explain how the conveyor belt applies force to the aircraft. Do you agree with the following statement?

-- The force the conveyor belt applies to the aircraft is due to friction in the wheel bearings and deformation of the tires making them not perfectly circular. --

If we agree on the above statement then the aircraft needs to extert enough force (engines pushing against the atmosphere) to overcome the conveyor belt's force before the plane can move. I think it's been established that once the plane generates enough lift via. airspeed that it can take off.

So, if you agree with the above (and please post your arguments if you don't) then the critical issue is how much force the conveyor can exert on the plane.

Since the conveyor can only exert force through friction in the bearings and wheel deformation there is no way it can extert enough force to overcome the jet's engines. If it could that would mean that jet's would never take off in the first place because they wouldn't be able to get moving, which obviously is not the case. The most that could happen would be that as the jet accellerates the wheels will be spinning at 2x the normal speed, which might cause some slight additional resistance. The only way the jet won't take off is if the wheel bearings fail because they are subjected to speeds outside of their design parameters.

On a side note, when people talk about the jet's "speed" are you talking air speed or ground (wheel) speed? If we are talking air speed then the jet would need to first move relative to the air to induce movement in the conveyor. If the argument is that the conveyor can extert enough force to stop the jet then we wind up with the jet's engines on full and neither it or the conveyor moving at all, which makes absolutely no sense.

- Matt

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#617313 - 29/12/06 01:30 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Moby, I'm afraid you're mistaken in this case. Your concept would have been correct if we were talking about a vehicle which is propelled down the runway by providing power to the wheels.

This is a completely different scenario. You must see that the wheels or the speed of the coveyor have absolutely no effect on the plane taking off.

It will fly.

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#617314 - 29/12/06 01:32 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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The plane has to gain airspeed to lift off. The force of gravity keeps it on the ground when it's stationary.

For it to move forward, it would have groundspeed. The air is calm. That means the air is equal to the ground in relation to the plane. If the plane cannot move on the ground, it cannot move in the air.

It cannot move on the ground, because the conveyor is negating it's forward movement.

It wouldn't matter if the wheels had a true no-friction connection to the plane. The conveyor is STILL going to counteract it.

It WOULD matter if the wheels were locked - the jets should have enough thrust to burn the wheels off (since the conveyor then wouldn't move, since the wheels aren't moving).

The wheels move because of the jets. Which means the jets in effect move the conveyor (since it matches the speed in opposite).
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617315 - 29/12/06 01:33 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by AHTOXA:
Moby, I'm afraid you're mistaken in this case. Your concept would have been correct if we were talking about a vehicle which is propelled down the runway by providing power to the wheels.

This is a completely different scenario. You must see that the wheels or the speed of the coveyor have absolutely no effect on the plane taking off.

It will fly.
Actually it's not.

What moves the wheels? (regardless of whether they are free spinning)
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617316 - 29/12/06 01:42 PM Re: Know that if you do not post in this thread today the human race may cease to exist
XPLORx4 Offline
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Registered: 23/03/01
Posts: 1906
Loc: San Jose, CA
Quote:
Originally posted by Mobycat:


What moves the wheels? (regardless of whether they are free spinning)
The plane's motion through SPACE (both on the ground and through AIR) sets the wheels in motion.

It's a given that as something that rests on the ground moves along the ground, it also moves through the air, too. It's the air that's being pushed through the engines, not the ground.
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#617317 - 29/12/06 01:44 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]

What moves the wheels? (regardless of whether they are free spinning)
The plane's motion through SPACE (both on the ground and through AIR) sets the wheels in motion.[/b]
But it's not moving through the space. The air is moving at the same speed as the plane - relative to the conveyor belt.

What moves?

Conveyor belt
Wheels

What does NOT move?

Ground
Air

Since the air is not moving, it cannot provide lift to overcome the downward force of gravity.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617318 - 29/12/06 01:46 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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OK.

Put one plane on one end of the conveyor belt.

Put another on the opposite end.

The conveyor belt counteracts the tires of one of them.

The other plane does not start it's engines. It will go with the conveyor belt.

Which will take off?

The one that has not started it's engines. The conveyor has pushed it through the air providing the pressure to cause lift.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617319 - 29/12/06 01:47 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Nothing moves the wheels. The wheels are simply freespinning. Yes, when the treadmill is moving backwards there's litte friection force applied to the wheels but way not enough to overcome the force of thrust delivered by the engines.

The force of thrus is completely not dependent on the speed of ground. No matter how fast the ground moves underneath, or whether it moves fast or slower, it would play no effect.

Let's say the same plane is on the same runway, BUT the direction of the runway movement would now be the same as the direction of the plane's take off.

Let's say that when the plane guns the jet engine the runway treadmill will spin at 400 mph ground speed (example). Let's assume that it would reach that speed instanteniously. Assume that there's no friction or rolling resistance.

The plane now is standing still and not moving anywhere. Engines are off. Now turn on the engines. The plane begins to take off.

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#617320 - 29/12/06 01:48 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by AHTOXA:
Nothing moves the wheels.
Wrong. The propulsion of the jets move the wheels.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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#617321 - 29/12/06 01:51 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Mobycat:
Quote:
Originally posted by AHTOXA:
[b]Nothing moves the wheels.
Wrong. The propulsion of the jets move the wheels.[/b]
Wrong. Wheels move due to plane accelerating down the runway. But the egines do NOT apply torque to the wheels thus spinning them. That's not a car. Maybe you're not really clear on how the jet engine works.

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#617322 - 29/12/06 01:54 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


Quote:
Originally posted by Mobycat:
The plane has to gain airspeed to lift off. The force of gravity keeps it on the ground when it's stationary.
Correct. Gravity also keeps the plane on the ground when it's moving. If it's moving at a great enough speed, gravity is counter-acted by aerodynamic lift.
Quote:
Originally posted by Mobycat:
For it to move forward, it would have groundspeed. The air is calm. That means the air is equal to the ground in relation to the plane. If the plane cannot move on the ground, it cannot move in the air.
It means the air is stationary, even if the conveyor moves under it. Here you are assuming that the aircraft cannot move on the ground.
Quote:
Originally posted by Mobycat:
It cannot move on the ground, because the conveyor is negating it's forward movement.
Incorrect. The conveyor cannot exert enough force or friction on the tires to counteract the thrust of a jet or prop.
Quote:
Originally posted by Mobycat:
It wouldn't matter if the wheels had a true no-friction connection to the plane. The conveyor is STILL going to counteract it.
The very purpose of the wheels is to reduce friction with the ground (conveyor, in this case). The purpose of the prop/jet is to create friction with the air. The props/jets create immense power and lots of friction with the air, creating forward movement. The wheels make it easier to move the aircraft over the surface. The surface moves in the opposite direction of the plane, with the conveyor, at twice the normal rate.
Quote:
Originally posted by Mobycat:
It WOULD matter if the wheels were locked - the jets should have enough thrust to burn the wheels off (since the conveyor then wouldn't move, since the wheels aren't moving).
The wheels being locked matters in another way-it is creating more friction with the conveyor/ground. This friction can still be overcome, though it is not safe. An aircraft under full power with brakes locked will move forward.
Quote:
Originally posted by Mobycat:
The wheels move because of the jets. Which means the jets in effect move the conveyor (since it matches the speed in opposite).
The jets do not move the wheels. The jets push the plane, and the friction with the ground causes the wheels to move. The original problem says nothing about the wheels pushing the conveyor, it says the conveyor matches the plane's speed.

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#617323 - 29/12/06 01:57 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


ok its going to take a blond to answer the question.. If you are in the gym and there happens to be a blond on the treadmill, she is running as fast as she can, and her hair is down.. Will her hair fly back like it would if she was running on the side of the road.. NO.. There is your answer..

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#617324 - 29/12/06 01:57 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Mobycat Offline
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Quote:
Originally posted by MattyX:
The conveyor cannot exert enough force or friction on the tires to counteract the thrust of a jet or prop.
Then the question is flawed. If it cannot exert enough force, it cannot match the speed. The question said it can.
_________________________
"Nature has constituted utility to man the standard and test of virtue. Men living in different countries, under different circumstances, different habits and regimens, may have different utilities; the same act, therefore, may be useful and consequently virtuous in one country which is injurious and vicious in another differently circumstanced" - Thomas Jefferson, moral relativist

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